Cytochrome c oxidase is an oligomeric protein complex isolated from the inner mitochondrial membrane. It is responsible for the terminal step in electron transport and the energy derived from this electron flow is coupled to the formation of adenosine triphosphate. This project is designed to provide structural information about the three-dimensional arrangement of the component parts of cytochrome c oxidase in wild-type and functional mutants of this enzyme isolated from yeast. This will be accomplished by: (1) chemically modifying specific cytochrome c oxidase sites with fluorescent and nonfluorescent chromophores; (2) reconstituting these labeled cytochrome c oxidase molecules into defined phospholipid vesicles; (3) the use of the technique of fluorescence resonance energy transfer to measure spacial relationships between these labeled sites, intrinsic chromophores and substrate; (4) determining changes in spacial relationship in functional mutants of cytochrome c oxidase; and (5) correlating these spacial relationships to chemical cross-linking procedures when possible.